1. Field of the Invention
This invention relates to a thermoplastic resin composition useful in cleaning an apparatus for shaping and fabricating thermoplastic resins.
2. Prior Arts
In the shaping of plastics, several kinds of treatment have been employed in order to get rid of the influence of preceding resin mixture remaining in the inside of shaping apparatus. Particularly, in the processing of colored products it is the actual state that troublesome workings such as cleaning of the inside of shaping apparatus, taking the apparatus apart for cleaning and accompanying suspension of a normal operation are inevitable at the time of change of color from preceding grade of relatively deep colored product such as blue or black colored to light colored product. In case of color change at the time of pelletizing, shaping by way of extrusion is taken as an example, such workings as suspension of an extruder operation, drawing out of a screw from a cylinder, cleaning of the screw and the inside of a cylinder by brushing or the like and reassembling the screw or the like are necessary. In the procedure in which a preceding kind of product is to be replaced by using some substitution resin, without drawing out of the screw, a large amount of resin is necessary for cleaning. Further, there is a problem of coloring inevitable in the following kinds of products because of the stain difficult to remove in the complicated construction parts within the extruder. In order to overcome these problems, compounds for clearing has been used. This means to make it easy to remove remaining material and complete the change of grade by using a small amount of substitution resin. Among compounds for cleaning, there is one in which a lubricant such as stearic acid or the like, is incorporated and there is also another in which acrylic resin having a higher melting temperature, etc. is used, but the former is attended with a drawback because cleaning effect is insufficient and the latter is attended with a drawback of stinking smell. Furthermore, there is another drawback that the reuse of substitution resin becomes difficult if these are mixed with the substitution resin. Further complex of operation is still unsettled e.g., compound must be used after dismantling a die, a breaker plate, a metal screen or the like because the viscosity of the melt of the latter is high. In addition, such a cleaning compound as those containing glass-fiber or the like is attended with drawbacks, e.g. substitution resin cannot be used again, and a screw or cylinder of shaping apparatus is liable to be worn out.
Further, it is possible to use in the cleaning of shaping and fabricating apparatus, a material obtained by blending powder of sodium alkylbenzenesulfonate with a substitution resin. However since sodium alkylbenzenesulfonate is so hygroscopic that a compound blended therewith is liable to become wet. On this account, there is a difficulty of handling such as bridge forming in the hopper of a shaping apparatus, a reduction of cleaning effect brought about by the absorbed moisture. Further in case of the fabrication of a thermoplastic resin composition to be carried out after those containing a large amount of a material such as calcium carbonate, magnesium silicate, barium sulfate, mica, etc. which is called as an inorganic filler or an inorganic pigment such as titanium oxide, ultramarine blue, red ocher or the like as a raw material, it is necessary to remove sufficiently the preceding kinds of resin mixture remaining in the shaping apparatus.
As evident from the foregoing description, an object of the present invention is to provide a cleaning thermoplastic resin composition, which makes it possible to get rid of the resin of precedent kinds of product remaining in the inside of shaping apparatus by simultaneously using a small amount of substitution resin through a simple and convenient operation.
As the result of study for cleaning-method, for shaping and fabricating apparatus in various way, we, the inventors of this application, have found that a resin composition obtained by adding a water repellent material such as liquid paraffin or a finely ground inorganic compound such as white carbon or the like to a neutral salt of an organic sulfonic acid such as sodium alkylbenzenesulfonate and mixing the resulting mixture with a thermoplastic resin, followed by pelletizing, have a superior cleaning effectiveness and completed the present invention.